Our findings suggested that the overall prevalence of both anxiety and depression decreased in past five years. However, such mental disorders are more frequent among certain groups of people such as young adults, women, unemployed and those who smoke cigarettes or opium, people with low physical activity and obesity; who were in need of more targeted interventions. We also found that the five-year incidence rate of anxiety is much higher than five-year incidence rate depression (15.0 vs. 3.9).
Overall, the findings of this study showed that currently 41.6% of the population had mild to severe levels of anxiety and 16.0% had mild to severe levels of depression, but both were significantly lower than corresponding values in phase 1 of the study (77.1% and 34.7%, respectively) . The reason for this is not clear for us but substantial increase in the provision of treatment facilities (including mental health services) by the government in the past five years may have played a role . In Iran, in recent years, the government has implemented a health promotion plan to cover treatment costs by offering more efficient health insurance to almost all Iranians. Social determinants such as poverty and unemployment are important factors for mental health  as it was shown that the prevalence of these disorders was highest in unemployed and lowest in office clerks (Table 1). The other probable influencing factor may be the agreement of the Joint Comprehensive Plan of Action in connection to Iran’s nuclear deal between Iran and the 5 + 1 countries, which raised the hope of lifting the economic sanctions against Iran and freeing billions of dollars in oil revenue and frozen assets. This plan was signed in April 2015 a few months after the commencement of the current study. The third possible explanation is that people have become more aware of common mental disorders. This may have been caused by the increase in the level of education in the country in the five years between the two phases. 18.6 percent of the participants in phase 1 had university education. This figure increased to 19.8 percent in phase 2. A reverse association was found between the level of education and the prevalence of anxiety and depression in the present study (Table 1).
The second finding of the study was that the prevalence and incidence rate of anxiety and depression were higher in women than in men. Although these results differ from some studies (some of which show no difference) [1, 2, 16], they are consistent with the findings of some others [17, 18]. After adjusting the impact of other covariates, there was a significant relationship between sex and anxiety and depression. The incidence of anxiety and depression in women was approximately twice that of men. The present findings seem to be consistent with other research which has found that sex is a contributing factor in anxiety and depression [19, 20]. This is also confirmed by our earlier observations . This result may be explained by the fact that women experience more positive and negative emotions and with greater intensity than men do .
The 5-year incidence rate of anxiety and depression symptoms were 15.0 and 3.9 persons/1000 person-years, respectively. The recorded incidence of anxiety and depression in women was slightly higher than it was in men. It is difficult to compare our findings with other incidence studies because of difference in socio-economic conditions, time span, and follow-up durations. Our findings seem to be consistent with other researches, which identified a greater incidence of anxiety and depression among women [16, 22]. The reduction of prevalence of anxiety and depression overall and in both genders during the last five years may be due to the low incidence rate of these disorders in this time period.
Surprisingly, despite the high prevalence of anxiety and depression in old age, one unanticipated finding was that the chance of anxiety and depression in the 15–24 age group was higher than it was in other groups. The possible mechanism may be that Iran is a country with a highly-educated young population. Unfortunately the rate of unemployment among educated people is high in Iran, and it was shown that employment is a very important factor in reducing anxiety and depression (Table 2),
Another risk factor associated with anxiety and depression was discordant marital life (separated/widowed). This finding is consistent with previous studies [20, 23, 24]. Loss of spouse is associated with a variety of adverse health outcomes including decreased physical well-being, increased mortality risk, and poor cognitive and functional health compared to married counterparts. Poor mental health is one of the most immediate responses to loss of spouse [25, 26].
Another important finding of this study was that university education is a protective factor against anxiety and depression. The fact that low level of education is an independent risk factor for mental and mood disorders and anxiety, has been shown in different studies [9, 20, 27]. Higher education improves self-esteem, vulnerability, and living standards . Moreover, educated people have more hope of finding a suitable job and sufficient income, which contributes greatly to their mental health in our community .
In line with previous studies, our results demonstrated that unemployment increases the chance of anxiety and depression [20, 29, 30]. Economically, unemployment status increases the risk of development and progression of psychiatric disorders and strong evidence is available in this regard for depression and anxiety disorders [31–33]. Unemployed people may develop some degree of anxiety and depression due to income inequality and the feeling of uselessness, failure, and incompetence , especially in countries with weak social security support and unemployment insurance like Iran. A longitudinal study showed a causal relation between socioeconomic position and depressive symptoms. It indicated that poor socioeconomic conditions lead to depression, which, in turn, can cause further damage to patients’ economic prospects .
The results illustrate that high physical activity decreased the chance of developing anxiety and depression. This can be due to the fact that exercising increases endorphin release in the brain. Endorphins have been proved to cause the feeling of happiness .
The results provided evidence that obesity may lead to anxiety and depression or be one of their consequences. Obese individuals had a significantly higher risk of developing major anxiety and depressive disorder over the 5-year follow-up period. There are a few studies that have tested obesity as a predictor of anxiety and depression, but most of them found that obesity or increased body mass index (BMI) were associated prospectively with anxiety and depression [37, 38]. Stigma and social prejudice against obesity may mediate this link [37, 39]. Functional impairment, which is greater among obese individuals , may also mediate the effect of weight status on anxiety and depression.
Cigarette smoking and opium use were highly comorbid with anxiety and depression (Table 1). This was consistent with the results of a review study that showed smoking was strongly associated with anxiety disorders and clinical depression . Sonntag et al. found that individuals with social phobia were more likely to also have nicotine dependence . Many individuals may smoke because of the presumed calming effects of nicotine and as a way of managing their anxiety. However smoking may rather serve to exacerbate symptoms by increasing the heart rate, blood pressure, and plasma norepinephrine and epinephrine . Some studies indicate that 70% of depressed people have a history of drug abuse and 75% of the people with a history of drug abuse suffer from depression. In fact, drug users face financial problems, unemployment, suicidal tendencies, and low social support, all of which can lead to anxiety and depression .
The collected data showed that hypertension was associated with an increased chance of anxiety, but not with an increased chance of depression. It is possible that labeling individuals as hypertensive may also play a role in the inter-relationships of stress, anxiety, and high BP [45, 46]. This is consistent with several other studies that have demonstrated higher psychological distress and lower well-being in hypertensive patients [45, 46]. Consistently, in a previous study, depressive disorder was associated with lower blood pressure .